Nitrogen in the livestock diet arises primarily from crude protein (CP) in feed. While needed for proper health and milk production, too much nitrogen in the diet results in an excess of nitrogen excreted into the environment. This excessive nitrogen excretion comes at a financial cost to the farmer who may be spending too much money on high protein feed or overfeeding, as well as an environmental cost. The dairy industry has explored ways of reducing excess dietary nitrogen by monitoring levels of excreted nitrogen in the form of urea in the milk and urine, and adjusting CP levels in the feed accordingly. However, farmers are concerned that by dropping CP levels too low, cows will consume less feed (sources of supplemental protein are typically very palatable) and as a result milk production will suffer. Currently, there is not a good method of optimizing efficient use of nitrogen in dairy herds.
In controlled experiments, the concentration of urea-N in milk, commonly referred to as milk urea-N (MUN), has been highly correlated with dietary crude protein (CP) level, nitrogen-use efficiency (NUE), and urinary urea-N excretion (UUNE). However, under field conditions, variations due to non-nutritional factors (e.g., sampling type, frequency of milking, milk production) and lack of information about the N intake on the day that data are sampled have lessened the value of MUN as a management tool.
Previous efforts have failed to recognize the importance of the ratio of milk urea-N yield (MUNY) and protein yield (PY) in economically feeding cattle without causing deleterious effects to the environment by the excretion of nitrogen. Moreover, existing methods are incapable of providing feedback to a user that would enable the adjustment of feeding practices within a day of measuring and interpreting data.
Accordingly, a need exists for methods that do not suffer from the mentioned shortcomings.